A conventional press includes a copper alloy liner adhered to a slide and an iron gib installed on the frame of the press. The slide is guided relative to the frame, while the liner and the gib slide against each other.
Lubricating oil is applied between the sliding surfaces of the liner and the gib. A clearance of approximately 0.05 mm is maintained between the liner and the gib. Uneven loading and the like may produce a line of contact between the liner and the gib, which may result in inadequate clearance and breaks in the oil film. This can damage the sliding surface and the main motor of the press.
It is particularly difficult to maintain proper clearance during precision pressing operations. Typical presses, such as two-point and four-point presses, handle larger slides by increasing the number of pressure-application points for applying eccentric loads. However, the dimensions of the crown, columns, bed, crank shaft, connecting rod, and the like must be precise in order to maintain levelness between the lower surface of the slide and the upper surface of the bolster. These components cannot be produced easily since they require a high level of precision. When the dimensions of these components are not sufficiently precise, a line of contact may form between the liner and the gib during operation under large eccentric loads.
Japanese patent application number 2000-193782 discloses a press in which a block with a spherical surface and a gib are interposed by a liner. The block and the gib can slide relative to each other via a V-shaped sliding surface. However, the V-shaped surfaces of the spherical-surface block and the gib are not easy to manufacture. The V-shaped surface on the spherical-surface block may spread apart under a large load, resulting in poor contact between the V-shaped surfaces. Japanese patent application number 2000-355350 discloses a device that is not affected by this problem.